KR102212380B1 - Method of oxidizing mercury in flue gas - Google Patents

Abstract

The present invention relates to a method for facilitating the collection of mercury from flue gases by converting elemental mercury into oxidized mercury and then trapping oxidized mercury. In one aspect, a method of removing mercury from a mercury-containing flue gas comprises introducing to the flue gas a source of sulfide in an amount effective to convert elemental mercury into gaseous oxidized mercury, and then gaseous oxidized mercury. It may include the step of collecting.

Description

How to Oxidize Mercury in Flue Gas {METHOD OF OXIDIZING MERCURY IN FLUE GAS}

The present invention relates to a method for reducing mercury emissions into the environment from the combustion of coal and/or other carbon-based fuels. In particular, the present disclosure relates to a method of converting elemental mercury into oxidized mercury and to trap the oxidized mercury.

Mercury is originally present in coal in concentrations ranging from 20 to 1000 ppb, and coal-fired power plants account for about 30% of the world's anthropogenic mercury emissions. All forms of mercury present in coal decompose during combustion into a highly volatile elemental form (Hg ⁰ ), which can be easily avoided by existing air quality control devices, typically present in power plants. However, if mercury can then be oxidized to the ionic form (Hg ^{2 +} ), it is much more easily captured by fly ash and adsorbents and/or scrubber liquids. Therefore, it is advantageous to maximize the conversion of elemental mercury to the oxidized form in order to promote capture.

The domestic technology used today for carrying out the conversion of elemental mercury to oxidized mercury uses bromine-containing additives such as calcium bromide (CaBr ₂ ), which have been shown to oxidize mercury much faster than natural chlorine present in many coals. To use. However, the use of bromine additives leads to the formation of hydrobromic acid (HBr), which is released from the stack or becomes soluble in scrubber fluid and wastewater, which is a problem for coal-fired utilities that use wetlands to treat wastewater. In addition, the problem of the use of bromine additives promoting high temperature corrosion mechanisms remains a publicly disclosed problem.

Accordingly, there is a continuing need for a method to reduce the release of mercury into the environment as well as prevent the release of pollutants resulting from the mercury containment process. More particularly, there is a need for technologies and products for oxidizing gaseous elemental mercury without forming harmful by-products together.

Summary of the invention

In one aspect, a method of removing mercury from a mercury-containing flue gas is described. The method comprises: a) introducing a source of sulfide into the flue gas in an amount effective to convert the gaseous elemental mercury into gaseous oxidized mercury; b) It involves the capture of gaseous oxidized mercury.

In certain embodiments, the source of sulfide can be a compound selected from the group consisting of sodium sulfide, copper sulfide and hydrogen sulfide. In certain embodiments, the sulfide source may be a polysulfide compound optionally selected from the group consisting of sodium polysulfide, ammonium polysulfide, potassium polysulfide and calcium polysulfide. In certain embodiments, the source of sulfide may be copper sulfide.

In certain embodiments, gaseous oxidized mercury is captured using a wet air scrubber. In another embodiment, gaseous oxidized mercury is captured using an adsorbent.

In certain embodiments, the sulfide source is introduced into a combustion process comprising flue gas. The combustion process may include an air-preheater, a boiler, and at least one device for trapping gaseous oxidized mercury. In certain embodiments, a source of sulfide can be introduced downstream of the boiler.

In certain embodiments, the sulfide source may be introduced into a flue gas having a temperature of greater than about 150°C, greater than about 300°C, or greater than about 1,000°C.

In certain embodiments, the method may be used in a coal fired power plant.

In yet another aspect, a method of removing mercury from a mercury-containing flue gas that has been passed through a wet flue gas desulfurizer is described. The method comprises: a) contacting a mercury-containing flue gas with a scrubber liquor of a desulfurizer, wherein the scrubber liquid contains a source of sulfide in an amount effective to convert elemental mercury into oxidized mercury; b) Includes the capture of oxidized mercury.

In some embodiments, the sulfide may be selected from inorganic sulfides such as sodium hydrogen sulfide, or organic sulfides such as polythiocarbamates, in addition to organic sulfides containing other functional groups, such as mercapto acetic acid, and 2,3-dimercaptopropanol. I can.

In certain embodiments, the sulfide source is a compound selected from the group consisting of sodium sulfide, copper sulfide, and hydrogen sulfide. In certain embodiments, the source of sulfide is a polysulfide compound. In certain embodiments, the polysulfide compound is selected from the group consisting of sodium polysulfide, ammonium polysulfide, potassium polysulfide, and calcium polysulfide. In certain embodiments, the sulfide source is copper sulfide or a copper sulfide/copper combination.

In certain embodiments, the scrubber liquid further comprises a mercury re-release additive. The mercury re-release additive is a polydithiocarbamic compound or an inorganic sulfide such as sodium hydrogen sulfide, or an organic sulfide such as polythiocarbamate or thiocarbamate, and an organic sulfide with polyfunctional groups such as 2,3- It may be selected from the group consisting of dimercaptopropanol and mercapto acetic acid.

In certain embodiments, the sulfide source comprises copper sulfide and the mercury re-release additive is a polydithiocarbamic compound.

1 is a diagram of a coal-fired power plant.
2 is a plot of the inlet and outlet mercury levels in flue gas measured before and after a spike of 1 gram of mercury sulfide powder.
3 is a plot of inlet and outlet mercury levels in flue gas measured before and after a spike of 2 grams of mercury sulfide powder.
4 is a plot of inlet and outlet mercury levels in flue gases measured before and after use of a copper sulfide adsorbent.

details

A method of converting elemental mercury into oxidized mercury is described herein.

In certain embodiments, the method of the invention comprises injecting a sulfide source into a mercury-containing flue gas stream to form mercury sulfide, and gaseous oxidized mercury species (e.g., HgCl ₂ ) resulting from the decomposition of mercury sulfide. It includes collecting.

Although the use of polysulfide compounds, such as sodium polysulfide, to capture mercury as solid mercury sulfide (HgS) has been previously reported, the inventors have surprisingly and unexpectedly found that mercury sulfide in the flue gas can be seen on a mercury monitor. It was found to decompose into gaseous species. Previous researchers have recognized that the polysulfide capture strategy is negatively influenced by increasing flue gas temperature and hydrochloric acid (HCl) concentration, but these researchers attributed the negative effect to HCl interactions with Na ₂ S ₄ rather than HgS. And this is an assumption that HgS is stable. Therefore, the instability of mercury sulfide in the flue gas fueled by coal may preclude the use of substances such as Na ₂ S ₄ and CuS as mercury adsorbents, but this description uses mercury sulfide, for example, a wet scrubber. Thus, there is provided a method of using a sulfide source in such a way that it decomposes into gaseous oxidized mercury species (e.g., HgCl ₂ , HgBr ₂ , or HgF ₂ ) that can be trapped and removed from the flue gas.

The method of the present invention provides an advantage over current processes for mercury capture in that mercury sequestration can be simplified with fewer capture procedures compared to current methods. By increasing the fraction of oxidized mercury in the flue gas, the method of the present invention increases the amount of mercury removal by activated carbon implants, wet scrubbers, and/or other mercury suppression techniques in place in the system. This improvement provides process efficiency and economic advantages over current methods and reduces the burden on the method of removing elemental mercury in place in the system in advance.

In certain embodiments, the method of the present invention comprises contacting a mercury-containing flue gas stream with a source of sulfide contained in a scrubber liquor and capturing the oxidized mercury formed in the scrubber liquor. The inventors have surprisingly and unexpectedly discovered that a scrubber liquid containing a source of sulfide can effectively convert elemental mercury into oxidized mercury for subsequent capture in the scrubber liquid.

1. Definition

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of dispute, this document, including definitions, will control. While preferred methods and materials are described below, methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples described herein are illustrative only and are not intended to be limiting.

The singular forms used in the specification and appended claims include plural quotations unless the context clearly dictates otherwise. As used herein, the terms “comprise”, “having”, “have”, “may”, “contain”, and variants thereof are open conversion phrases that do not exclude the possibility of further action or structure ( open-ended transitional phrase), term or word. This description also contemplates other embodiments, "comprising", "consisting of" and "essentially including", which are embodiments or elements presented herein, whether expressly stated or not.

As used herein, the term "mercury re-release" refers to a phenomenon in which the water-soluble oxidized mercury (Hg ^{2 +} ) undergoes chemical reduction to the water-insoluble element mercury (Hg ⁰ ) in a wet flue gas desulfurization (WFGD) scrubber. The reduction is believed to occur due to the reaction between mercury ions and sulfite ions present in the WFGD liquid. Since elemental mercury is insoluble in water, elemental mercury is released in the gaseous phase from the scrubber. Accordingly, the concentration of elemental mercury in the flue gas discharged from the scrubber is higher than the concentration of elemental mercury entering the scrubber.

The term "percent mercury rerelease" as used herein refers to:

식 1

Equation 1

In the above equation, "outlet" represents the measurement of mercury in the stack gas, "inlet" represents the gas concentration at the inlet to the WFGD, "0" represents the concentration of elemental mercury in the gas, and "T" represents the total concentration of mercury in the gas. Show. The “outlet” measurement may refer to a measurement of mercury gas at any point after the gas has been released from the WFGD.

The term "percent mercury oxidation" as used herein refers to:

식 2

Equation 2

In the above formula, superscript and subscript have the same meaning as defined in Equation 1 above.

The term “percent mercury capture” as used herein refers to:

식 3

Equation 3

In the above formula, superscript and subscript have the same meaning as defined in Equation 1 above.

2. Elemental mercury Gaseous With oxidized mercury Converting Way

Described herein is a method of converting elemental mercury into oxidized mercury to facilitate mercury removal from combustion gases. This method involves contacting elemental mercury with a sulfide-source to produce oxidized mercury that can then be captured.

The method of the present invention can be used in any process where it is desired to remove mercury from flue gases. For example, the method of the present invention includes waste incineration plants (e.g. household waste, hazardous waste, or sewage sludge incineration plants), power plants (e.g. bituminous coal-fired, or lignite-fired power plants), and other plants for high-temperature processes. (E.g. cement firing), and high-temperature flaps or integrated (multi-stage) high-temperature plants that are burned with the waste (e.g., power plants, or cement rotary kiln with upstream waste pyrolysis or waste gasification) kiln)).

The method of the present invention can be used for any dimension process. This method is for example 15×10 ³ m ³ STP db/h for sewage sludge incineration, or 50×10 ³ m ³ STP db/h, eg in hazardous waste incinerators, or, for example, for domestic use. In waste incineration, it can be used in processes with flue gas volume flow rates of 150 × 10 ³ m ³ STP db/h, and also in large power plants with, for example, 2-3 × 10 ⁶ m ³ STP db/h.

Sources of sulfides useful in the process of the present invention include copper sulfide (CuS), copper sulfide/copper combination, sodium sulfide (Na ₂ S), hydrates of sodium sulfide (e.g. Na ₂ S 9H ₂ O), sodium poly Sulfide (e.g. sodium tetrasulfide), calcium polysulfide, potassium polysulfide, ammonium polysulfide, sodium hydrogen sulfide, hydrogen sulfide, carbon disulfide, polythiocarbamate, polydithiocarbamic compound, 2,3-dimer Captopropanol, mercapto acetic acid, or any combination thereof, including, but not limited to. In certain embodiments, the sulfide source may be a blend comprising copper sulfide and polysulfide. In certain embodiments, the sulfide source may be an adsorbent comprising copper and/or copper sulfide, polysulfide, and silica.

a. Sulfide Introduction of the source of flue gas

In one aspect, described herein is a method of converting elemental mercury in a flue gas to gaseous oxidized mercury. The inventors have unexpectedly and surprisingly discovered that a source of sulfide can be used to convert elemental mercury into gaseous oxidized mercury through a mercury sulfide decomposition process. Introduction of a sulfide source into a mercury-containing flue gas produces mercury sulfide, which is then gaseous oxidized mercury (e.g., HgCl ₂ , HgBr ₂ , or) that can be removed from the flue gas before exiting the stack. HgF ₂ ) is decomposed.

In certain embodiments, the method of the present invention comprises (a) providing a source of sulfide to a coal fired flue gas to form mercury sulfide by reacting the source of sulfide with elemental mercury present in the gas; (b) the capture of gaseous oxidized mercury formed from the decomposition of mercury sulfide. The sulfide source can be any sulfide source as described above. In certain embodiments, the sulfide source is copper sulfide or a copper sulfide/copper combination.

The sulfide source may be provided as flue gas at any suitable location in a combustion process involving flue gas. In general, higher flue gas temperatures and longer residence times promote the decomposition of mercury sulfide produced by reaction of the sulfide source with elemental mercury. During the introduction of the sulfide source, the temperature of the flue gas was 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850. It may be greater than ℃, 900 ℃, or 950 ℃. In certain embodiments, the flue gas is about 150°C to about 1000°C, about 200°C to about 1000°C, about 250°C to about 1000°C, about 300°C to about 1000°C, about 350°C to about 1000°C, about 400 ℃ to about 1000 ℃, about 450 ℃ to about 1000 ℃, about 500 ℃ to about 1000 ℃, about 550 ℃ to about 1000 ℃, about 600 ℃ to about 1000 ℃, about 650 ℃ to about 1000 ℃, about 700 ℃ to It is in the range of about 1000°C, about 750°C to about 1000°C, about 800°C to about 1000°C, about 850°C to about 1000°C, about 900°C to about 1000°C, or about 950°C to about 1000°C.

The sulfide source can be supplied to the flue gas by any suitable method known in the art. In certain embodiments, the source of sulfide can be injected into the aqueous solution by a nozzle facing the combustion system. The aqueous solution can be co-injected with air, recycled flue gas, nitrogen or another carrier gas to increase the permeability of the sulfide source through the flue gas path and improve the mixing of the sulfide source with the flue gas. For example, the sulfide source can be with a carrier gas such as nitrogen or air; With hot steam; With slurries blended with other additives (eg, sulfur oxide adsorbent); It can be provided to the flue gas through a fixed bed device, through which the flue gas is passed along with an inorganic adsorbent such as aluminosilicate, silica containing material or zeolite; With activated carbon; Through a lance; Through a conveyor belt; Or it is passed through an aqueous solution.

The gaseous oxidized mercury produced by the decomposition of the produced mercury sulfide can be captured by devices and processes known in the art. In certain embodiments, one or more scrubbers currently used in the gaseous oxidized mercury industry (e.g., spray towers, jet bubblers, and co-current packed towers) are used. Is captured. In certain embodiments, gaseous oxidized mercury is captured using one or more adsorbents. In certain embodiments, one or more of the gaseous oxidized mercury is captured using one or more scrubbers with an adsorbent.

1 shows an exemplary coal fired power plant adaptable with the method of the present invention. The power plant includes a boiler 10, a selective catalytic reduction device 20, an air preheater 30, a particulate suppression device (particulate suppression device) 40 (for example, an electrostatic precipitator), a scrubber ( 50) (e.g., a wet or dry flue gas desulpherization system), and a discharge stack 60. Coal-fired power plants may have additional components as well as multiple devices of the same or similar type (eg, multiple particulate suppression devices).

The sulfide source can be injected into the system of FIG. 1 at any suitable point. In certain embodiments, a source of sulfide may be injected into the boiler 10 as at point B. In certain embodiments, a source of sulfide may be injected upstream of the air preheater 30 as at point C. In certain embodiments, a source of sulfide may be injected downstream of the air preheater 30, such as at point D. Alternative setups are possible where any one of the system components (e.g. SCR, air preheater, particulate suppression device) can suitably be configured upstream or downstream to each other, and the sulfide introduction point is It is to be understood that it can be adjusted to take into account these alternative configurations.

b. Sulfide Source of With scrubber fluid Introduction

In another aspect, described herein is a method of converting elemental mercury to oxidized mercury in a wet scrubber. The inventors have unexpectedly and surprisingly discovered that elemental mercury passing through a wet scrubber can be used to convert elemental mercury into oxidized mercury by contacting it with a source of sulfide, a source of sulfide contained in the scrubber liquid. Oxidized mercury is trapped in the scrubber fluid and can be removed from the flue gas prior to exiting the stack.

In certain embodiments, the method of the present invention comprises (a) contacting a mercury-containing flue gas with a scrubber liquid comprising a source of sulfide in an amount effective to convert elemental mercury into oxidized mercury in a wet flue gas desulfurizer and ; (b) It involves trapping oxidized mercury. The sulfide source can be any sulfide source as described above. In certain embodiments, the sulfide source includes copper sulfide, copper sulfide/copper combination, or polysulfide.

The method can be used with any scrubber currently used in the industry, including spray towers, jet bubblers, and co-current packed towers. These types of particulate suppression devices are presented by way of example and are not meant to indicate or imply any limitations.

In certain embodiments, the configuration according to FIG. 1 can be applied to the method. Any additional ingredients that are introduced or blended concurrently with the sulfide source and the sulfide feed can be introduced, for example at points E and/or F.

The source of sulfide is introduced into the scrubber, whereby it can be introduced into the scrubber fluid via several routes. For example, the sulfide source may be added to a virgin limestone or lime slurry prior to being added to the scrubber, to the recycle loop of scrubber liquor, or to the "low solids" that is returned to the scrubber from the scrubber purge stream. The addition of a sulfide source, such as copper sulfide, includes, but is not limited to, lime or limestone slurry or make-up water for scrubber liquor at any suitable location in the scrubber process, in whole or in part (i.e. , Single point of supply or multiple points of supply).

In certain embodiments, a source of sulfide may be added to the wet scrubber via a "low solids" liquid return. Some of the liquor is generally removed continuously from the scrubber for the purpose of separating reaction by-products from unused lime or limestone. One of the currently used separation means is centrifugation. In this process, the scrubber liquor is separated into "high solids" and "low solids" streams. The high solids stream is diverted to wastewater treatment. The low solids fraction is returned to a wet scrubber and can be considered a "reclaimed" dilution. The sulfide source can be easily added to the recycled low solids stream prior to being returned to the scrubber.

In certain embodiments, the source of sulfide can be added to the wet scrubber via a “virgin liquor”. The raw liquor is an aqueous dispersion of lime or limestone prior to exposure to flue gas and is used to add fresh lime or limestone while maintaining the scrubber liquor level and the efficiency of wet FGD. It is produced by dispersing lime or limestone in water. Here, the sulfide source may be added directly to either the dispersed water or the raw liquid. In certain embodiments, the source of sulfide may be added to the scrubber fluid injected directly into the flue gas prior to scrubbing for the purpose of controlling the relative humidity of the flue gas or its temperature (e.g., at point E in FIG. 1).

The scrubber liquid referred to herein may be an aqueous dispersion of calcium carbonate (limestone) or calcium oxide (lime) used in a wet flue gas desulfurizer to capture SO _x emissions. The scrubber liquid may also contain other additives such as magnesium and low molecular weight organic acids, which serve to enhance sulfur capture. An example of such an additive is a mixture of low molecular weight organic acids known as dibasic acids (DBA). DBA consists of a blend of adipic acid, succinic acid and glutaric acid. Each of these organic acids can also be used individually. In addition, another low molecular weight organic acid that can be used to improve sulfur capture in wet scrubbers is formic acid. Finally, the scrubber liquor may also contain lime or a by-product of the interaction between limestone and sulfur species, which leads to the presence of varying amounts of calcium sulfite or calcium sulfate. The scrubber liquid may include a constituent liquid, a conveyance liquid, a recycle liquid, a raw liquid, and/or a liquid directly injected into the flue gas.

In certain embodiments, the scrubber liquid may further include a mercury re-release inhibitory additive. The mercury re-release inhibitory additive may be introduced into the scrubber fluid separately from the sulfide source, and/or may be blended with the sulfide source and/or may be supplied to the scrubber fluid concurrently with the sulfide source (e.g., co-feed).

Mercury re-emission inhibiting additives that can be used in the process of the present invention include any additive suitable for reducing and/or inhibiting mercury re-emissions from combustion processes, in particular scrubber fluids. In certain embodiments, the mercury re-release inhibitory additive is a poly-dithiocarbamic compound (eg, MerControl 8034, also referred to herein as “poly-DTC”), or another sulfur-containing additive, such as sodium sulfide. , Sodium hydrogen sulfide, sodium bisulfide, or poly-sulfide. In certain embodiments, the mercury re-release inhibitory additive may be diethyldithiocarbamate or a sodium salt thereof. In certain embodiments, the mercury re-release inhibitory additive may be dimethyldithiocarbamate or a sodium salt thereof. In certain embodiments, the mercury re-release inhibitory additive may be an inorganic poly-sulfide or blend, such as PRAVO, a product from Vosteen. In certain embodiments, the mercury re-release additive is of 1,3,5-triazine-2,4,6(1H,3H,5H)-trithione (also referred to as trimercapto-S-triazine). Sodium or calcium salt, such as TMT-15, a product from Degussa. In certain embodiments, the mercury re-release inhibitory additive may be activated carbon as described in US Pat. No. 7,727,307 B2. In certain embodiments, the mercury re-release inhibitory additive may be dithiol, dithiolane, or a thiol having a single thiol group and an oxygen or hydroxyl group. Suitable dithiols include, but are not limited to, 2,3-dimercaptopropanol, dimercaptosuccinic acid, and 1,8-octanedithiol. Suitable dithiolanes include, but are not limited to, 1,2-dithiolane-3-valeric acid and 2-methyl 1,3-dithiolane. Suitable thiols include, but are not limited to mercaptoacetic acid and its sodium salt. In certain embodiments, combinations of mercury re-release inhibitory additives may be used. In one preferred embodiment, the mercury re-release inhibitory additive comprises a poly-dithiocarbamic compound.

In certain embodiments, the mercury re-release inhibitory additive has a molecular weight of 500 to 10,000 to prevent the re-release of mercury over the wFGD and contains 5 to 55 mole percent dithiocarbamate salt groups of water-soluble ethylene dichloride ammonia. It can be a polymer. Polymers can be prepared by reaction of ethylene dichloride with ammonia to give polyamines or polyimines. The polyamine or polyimine may have a molecular weight range of 500-100,000. In a preferred embodiment, the molecular weight may be 1,500 to 10,000, and the most preferred molecular weight range is 1,500 to 5,000. The dithiocarbamate group of the polymer can be introduced by reacting a polyamine or polyimine with carbon disulfide to form a polydithiocarbamic acid or salt thereof. This reaction is preferably carried out in a solvent such as water or alcohol at a temperature of 30° C. to 100° C. for a period ranging from 1 to 10 hours. Excellent conversion can be obtained at temperatures of 40° C. to 70° C. for 2 to 5 hours. The mole percent of the dithiocarbamate salt groups in the final polymer can be in the range of 5 to 55%, 20 to 40 mole%, or 25 to 30 mole%. Salts include, but are not limited to, alkalis and alkaline earths such as sodium, lithium, potassium or calcium. The final polymer can be applied to the combustion process in a ratio of 1:1 to 2000:1 copolymer weight to the weight of mercury captured. A preferred ratio may be 5:1 to 1000:1, more preferably 5:1 to 500:1.

In certain embodiments, the mercury re-release inhibitory additive may be a composition comprising a polymer derived from at least two monomers: acrylic-x (acrylic-x) and alkylamine, wherein acrylic-x has the formula:

In the above formula, X = or, OH and a salt thereof, or NHR ² , R ¹ and R ² are H or an alkyl or aryl group, R is an alkyl or aryl group, and the molecular weight of the polymer is 500 to 200,000, wherein The polymer is modified to contain functional groups capable of scavenging one or more compositions containing one or more metals. Metals can include zero-valent, monovalent, and polyvalent metals. The metal may or may not be ligated by organic or inorganic compounds. In addition, the metal can be radioactive and non-radioactive. Examples include, but are not limited to, transition metals and heavy metals. Specific metals may include copper, nickel, zinc, lead, mercury, cadmium, silver, iron, manganese, palladium, platinum, strontium, selenium, arsenic, cobalt, and gold, but are not limited thereto.

The molecular weight of the acrylic-x and alkylamine derived polymers can vary. For example, the target species/application for the polymer may be one consideration. Another factor may be monomer selection. The molecular weight can be calculated by several methods known to those skilled in the art. For example, size exclusion chromatography, discussed in the examples below, may be used. When a molecular weight is mentioned, otherwise referred to as the polymer backbone, it is indicative of the molecular weight for the unmodified polymer. Functional groups added to the backbone are not part of the calculation. Thus, the molecular weight of the polymer with functional groups can greatly exceed the molecular weight range. In one embodiment, the molecular weight of the polymer is 1,000 to 16,000. In another embodiment, the molecular weight of the polymer is 1,500 to 8,000.

Several functional groups can be used for metal scavenging. The following terms will be well understood by those skilled in the art: The polymer is modified to contain functional groups capable of scavenging one or more compositions containing one or more metals. More specifically, the polymer is modified to contain functional groups capable of binding metals. In one embodiment, the functional group contains a sulfide containing chemical structure. In another embodiment, the functional group is a dithiocarbamate salt group. In another embodiment, the functional group is at least one of the following: alkylene phosphate group, alkylene carboxylic acid and salts thereof, oxime group, amidooxime group, dithiocarbamic acid and salts thereof, hydroxamic acid, or nitro Gen oxide. The molar amount of functional groups relative to the total amine contained in the unmodified polymer may also vary. For example, the reaction of an acrylic acid/TEPA copolymer in a 1.0:1.0 molar ratio containing 3.0 molar equivalents of carbon disulfide to 4 molar equivalents of amine per repeating unit after polymerization, contains 75 mol% dithiocarbamate salt groups. It will form a polymer that has been modified to do so. That is, 75% of the total amines of the unmodified polymer have been converted to dithiocarbamate salt groups. In one embodiment, the polymer may have 5 to 100 mole percent dithiocarbamate salt groups. In a further embodiment, the polymer has 25 to 90 mole percent dithiocarbamate salt groups. In a further embodiment, the polymer has 55 to 80 mole percent dithiocarbamate salt groups.

The monomer selection will depend on the desired acrylic-x and alkylamine derived polymer. In one embodiment, the alkylamine is at least one of: ethyleneamine, polyethylenepolyamine, ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetraamine (TETA), tetraethylenephetamine (TEPA), and penta. Ethylenehexamine (PEHA). In another embodiment, acrylic-x is at least one of: methyl acrylate, methyl methacrylate, ethyl acrylate, and ethyl methacrylate, propyl acrylate, and propyl methacrylate. In another embodiment, acrylic-x is at least one of: acrylic acid and salts thereof, methacrylic acid and salts thereof, acrylamide, and methacrylamide. The molar ratio of the monomers constituting the polymer, in particular acrylic-x and alkylamine, varies and can depend on the desired polymer product to be formed. The molar ratio used is defined as the molar ratio of acrylic-x divided by the moles of alkylamine. In one embodiment, the molar ratio between acrylic-x and alkylamine is 0.85 to 1.5. In another embodiment, the molar ratio between acrylic-x and alkylamine is between 1.0 and 1.2. Several combinations of acrylic-x and alkylamines as well as the relevant molecular weight of the polymer are encompassed by the present invention. In one embodiment, acrylic-x is an acrylic acid ester and the alkylamine is PEHA or TEPA or DETA or TETA or EDA. In a further embodiment, the molar ratio of acrylic-x and alkylamine is 0.85 to 1.5. In yet another further embodiment, the molecular weight may comprise a range of 500 to 200,000, 1,000 to 16,000, or 1,500 to 8,000. In another further embodiment, the acrylic acid ester can be at least one of the following: methyl acrylate, methyl methacrylate, ethyl acrylate, and ethyl methacrylate, propyl acrylate, and propyl methacrylate, which are PEHA Or TEPA or DETA or TETA or EDA-containing alkylamine. In another further embodiment, the polymer formed is modified to contain dithiocarbamate salt groups in the following ranges: 5 to 100 mole percent, 25 to 90 mole percent, or 55 to 80 mole percent. In another embodiment, acrylic-x is acryl amide and alkylamine is TEPA or DETA or TETA or EDA. In a further embodiment, the molar ratio between acrylic-x and alkylamine is between 0.85 and 1.5. In yet another further embodiment, the molecular weight may comprise a range of 500 to 200,000, 1,000 to 16,000, or 1,500 to 8,000. In yet another further embodiment, the acrylamide may be at least one of acrylamide and methacrylamide, or a combination thereof, combined with at least one of PEHA or TEPA or DETA or alkylamine comprising TETA or EDA. In another further embodiment, the polymer formed is modified to contain dithiocarbamate salt groups in the following ranges: 5 to 100 mole percent, 25 to 90 mole percent, or 55 to 80 mole percent. In another embodiment, acrylic-x is acrylic acid and salts thereof and the alkylamine is PEHA or TEPA or DETA or TETA or EDA. In a further embodiment, the molar ratio between acrylic-x and alkylamine is between 0.85 and 1.5. In yet another further embodiment, the molecular weight may comprise a range of 500 to 200,000, 1,000 to 16,000, or 1,500 to 8,000. In yet another further embodiment, the acrylic acid may be any one of acrylic acid or a salt thereof and methacrylic acid or a salt thereof, or a combination thereof, combined with at least one of TEPA or DETA or an alkylamine comprising TETA or EDA. . In another further embodiment, the polymer formed is modified to contain dithiocarbamate salt groups in the following ranges: 5 to 100 mole percent, 25 to 90 mole percent, or 55 to 80 mole percent.

Additional monomers may be incorporated into the polymer backbone composed of the constituent monomers, acrylic-x and alkylamine. Polymer scheme considerations can be used to create the basic polymer backbone chain. Several different synthetic methods can be used to functionalize the polymer with, for example, dithiocarbamate and/or other nonmetallic scavenging functional groups. Those of skill in the art can functionalize the polymer without undue experimentation. In certain embodiments, the composition may be formulated with a water soluble ethylene dichloride ammonia polymer having a molecular weight of 500 to 100,000, containing 5 to 55 mole percent dithiocarbamate salt groups. In one embodiment, the polymer has a molecular weight of 1,500 to 10,000 and contains 15 to 50 mole percent dithiocarbamate salt groups. In a preferred embodiment, the molecular weight of the polymer is 1,500 to 5,000 and contains 30 to 55 mole% of dithiocarbamate salt groups. In certain embodiments, the composition comprises other small molecule sulfide precipitates such as sodium sulfide, sodium hydrogen sulfide, TMT-15® (sodium or calcium salt of trimercapto-S-triazine), dimethyldithiocarbamate, and/or di. It can be formulated with ethyldithiocarbamate.

The dosages of the described mercury re-release inhibitory additives can be varied as needed to reduce or prevent mercury re-release. Process medium quality and amount of process medium treatment agent are binding factors, which can be considered by those skilled in the art in choosing a dosage. Jar test analysis is a representative example of what is used as a basis for determining the dosage required to achieve effective metal removal in relation to process water media, eg waste water. In one embodiment, the amount of the mercury redemission inhibiting additive for effectively removing metals from contaminated water is dithiocarbamate within the range of 0.2 to 2 moles per mole of metal contained in water, or within the range of 1 to 2 moles per mole of metal. It may be a dithiocarbamate. According to one embodiment, the dosage of metal removal polymer required to chelate and precipitate 100 ml of 18 ppm water soluble copper to about 1 ppm or less is 0.011 gm (11.0 mg) of polymer. The formed metal polymer complex self-aggregates and settles rapidly. These aggregates are easily separated from the treated water. Regarding the application of the polymer to a gas system, such as a flue gas, the polymer is dosed incrementally, and the capture rate for certain metals, such as mercury, can be calculated by techniques known in the art. . In certain embodiments, a mercury re-release inhibitory additive, such as a water-soluble ethylene dichloride ammonia polymer with dithiocarbamate salt groups, can be applied to the scrubber solution in a ratio of 1:1 to 2000:1 polymer weight to the weight of mercury captured. . One preferred dosage ratio is 5:1 to 1000:1, more preferably 5:1 to 500:1.

c. Sulfide Flue gas from the source and With scrubber fluid Introduction

In another aspect, described herein is a method of converting elemental mercury into oxidized mercury by contacting elemental mercury in a flue gas with a source of sulfide and passing elemental mercury through a wet scrubber with a source of sulfide.

In certain embodiments, the method of the invention comprises: (a) introducing a source of sulfide into a mercury-containing flue gas in an amount effective to convert elemental mercury into gaseous oxidized mercury; (b) contacting the mercury-containing flue gas with a scrubber liquid of a wet flue gas desulfurizer, the scrubber liquid comprising a source of sulfide in an amount effective to convert elemental mercury into oxidized mercury; (c) It involves the capture of oxidized mercury. The sulfide source can be any sulfide source as described above. Sulfide is introduced into the device and process as described above, and can follow the method described above.

In certain embodiments, the scrubber liquor may further comprise a mercury re-release inhibitory additive as described herein. The mercury re-release inhibitory additive may be introduced into the scrubber fluid separately from the sulfide source and/or may be blended with the sulfide source and/or may be provided to the scrubber fluid concurrently with the sulfide source (e.g., co-feed).

3. Example

Example One

Formation of gaseous oxidized mercury from mercury sulfide

The instability of mercury sulfide was demonstrated by two drops of pure mercury sulfide powder in the flue gas duct in front of an electrostatic precipitator (ESP) where mercury sulfide was trapped and exposed to hot flue gas.

As shown in Figs. 2 and 3, each time the outlet mercury level is higher than the inlet level after administration of pure mercury sulfide powder. The increase in elemental mercury levels seen during these experiments was not accompanied, suggesting that the gaseous form of the developed mercury was clearly present in an oxidized form. Among the known possible mercury(II) compounds that are believed to be capable of forming, mercury chloride (HgCl ₂ ) and mercury bromide (HgBr ₂ ) will be sufficiently stable and volatile to be measured by a mercury monitor. Without being bound by theory, since coal almost inevitably contains much more chlorine than bromine, even though either product is an acceptable ionic form for the subsequent capture and removal of mercury from the flue gas, the final product is almost entirely. It is believed to be mercury chloride.

Example 2

Injection of sulfide source Pre-APH

As shown in Figure 4, copper sulfide was injected before a pre air-preheater, resulting in an increase in the percentage of oxidized (measured in the stack) mercury from 48% to 85%. These results show that the introduction of a source of sulfide into the flue gas is an effective amount to convert elemental mercury into oxidized mercury, thereby facilitating the removal of mercury from the flue gas through a system (e.g., wFGD) in place beforehand. Suggests. In Figure 4, TX15047 represents a dry MerControl 6012. The basic formulation from CHARMS is about 68% colloidal silica; About 9.67% sulfur; About 7.21% copper compound; And about 15.13% water.

Example 3

Formation of oxidized mercury from polysulfide species

A bench top experiment using an Ohio Lumex spectrometer has demonstrated that polysulfide species can oxidize elemental mercury. An additional impinger was included in the setup including the RP-915+ spectrometer to allow the gas to bubble through the additional solution. The use of SnCl ₂ caused the ionic mercury present in the 500 ppt standard solution to be reduced to elemental mercury and released into the vapor phase to migrate through the impinger train. In the 500 ppt Hg baseline experiment, an additional impinger contained 25.2 g deionized water. That is, further oxidation or collection was not possible. To determine the mercury oxidation capacity of the polysulfide, 3.25 g of a 28% calcium polysulfide solution was added to an additional impinger and the 500 ppt Hg standard was restarted. All experiments were conducted 3 times. As shown in Table 1, a 20% reduction in mercury reaching the detector was observed with polysulfide. Thus, the source of sulfide contained in the scrubber liquid can facilitate the oxidation and capture of mercury. Mercury re-release additives can be combined with the use of sulfide-species to further reduce mercury release.

Table 1

Any range presented by either absolute or approximate terms is intended to include both, and any definitions used herein are intended to be clarified, not limiting. Although the numerical ranges and parameters referring to the broad scope of the present invention are approximations, the numerical values referred to in specific examples are recorded as accurately as possible. However, some numerical values inherently necessarily have certain errors resulting from the standard deviations present in their respective test measurements. In addition, all ranges described herein are to be understood as including any subranges and all subranges (including all parts and all values) contained therein.

In addition, the present invention includes any and all possible combinations of some or all of the various embodiments described herein. Any and all patents, patent applications, scientific papers, and other references cited herein, and any references cited therein, are incorporated herein by reference in their entirety. In addition, it should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without reducing its intended advantages. Therefore, such changes and modifications are intended to be covered by the appended claims.

Claims (19)

A method for removing mercury from a mercury-containing flue gas, comprising:
a) introducing a source of sulfide into the flue gas to form mercury sulfide, and the mercury sulfide is then decomposed into gaseous oxidized mercury containing at least one of HgCl ₂ , HgBr ₂ , and HgF ₂ ; And
b) capturing gaseous oxidized mercury. The method of claim 1, wherein the sulfide source is a compound selected from the group consisting of sodium sulfide, copper sulfide, and hydrogen sulfide. The method of claim 1, wherein the source of sulfide is a polysulfide compound. 4. The method of claim 3, wherein the polysulfide compound is selected from the group consisting of sodium polysulfide, ammonium polysulfide, potassium polysulfide, and calcium polysulfide. The method of claim 1, wherein the sulfide source is copper sulfide or a copper sulfide/copper combination. The method of claim 1, wherein step b) comprises capturing gaseous oxidized mercury using a wet flue gas desulfurizer (wFGD). The method of claim 1, wherein step b) comprises capturing gaseous oxidized mercury using an adsorbent. The method of claim 1, wherein the sulfide source is introduced into a combustion process comprising flue gas, the combustion process comprises an air-preheater, a boiler, and at least one device for capturing gaseous oxidized mercury, and The method introduced downstream of the boiler. The method of claim 1, wherein the source of sulfide is introduced into a flue gas having a temperature greater than 150°C. The method of claim 1, wherein the source of sulfide is introduced into a flue gas having a temperature above 300°C. The method of claim 1, wherein the method is used in a coal fired power plant. A method for removing mercury from a mercury-containing flue gas, comprising:
a) mercury-containing flue gas is brought into contact with a scrubber liquor containing a sulfide source of a wet flue gas desulfurizer to form mercury sulfide, and at least one of HgCl ₂ , HgBr ₂ , and HgF ₂ Decomposing into oxidized mercury comprising a; And
b) A method comprising trapping oxidized mercury. 13. The method of claim 12, wherein the sulfide source is a compound selected from the group consisting of sodium sulfide, copper sulfide, and hydrogen sulfide. 13. The method of claim 12, wherein the source of sulfide is a polysulfide compound. 15. The method of claim 14, wherein the polysulfide compound is selected from the group consisting of sodium polysulfide, ammonium polysulfide, potassium polysulfide, and calcium polysulfide. 13. The method of claim 12, wherein the sulfide source is copper sulfide or a copper sulfide/copper combination. 13. The method of claim 12, wherein the scrubber liquid further comprises a mercury re-release inhibitor. 18. The method of claim 17, wherein the mercury re-release inhibitory additive is a polydithiocarbamic compound. 18. The method of claim 17, wherein the source of sulfide comprises copper sulfide and the mercury re-release inhibitory additive is a polydithiocarbamic compound.

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